Effects of Doping and/or Atmosphere on the ElectricalConductivity of Li4Ti5O12

Tantalum (Ta) doping in lithium titanium oxide, Li4Ti5O12 (Li4Ti4.95Ta0.05O12), as function of different heat-treatment atmospheres (oxidizing/reducing) was investigated and compared to Li4Ti5O12 to determine its effect on electrical conductivity and rate capability. The ionic conductivity value of the white colored Li4Ti4.95Ta0.05O12 heated under an oxidizing atmosphere was ~3 x 10-8 S/cm with a DC electronic conductivity value of ~1 x 10-9 S/cm. These values are similar to values observed for Li4Ti5O12 heated under the same oxidizing atmosphere. These results suggest that both materials are predominately ionic conductors, with the extra charge of Ta compensated by a lattice defect, most likely titanium (Ti) vacancies. For the case of Li4Ti4.95Ta0.05O12 heated under a reducing atmosphere, it was purple colored with an electronic conductivity value of ~1 x 10-3 S/cm. Li4Ti5O12 heated under a reducing atmosphere was also purple colored with an electronic conductivity value of ~3 x 10-5 S/cm. These results suggest both of these materials are predominately electronic conductors where the electronic conductivity is a result of the reduction of some Ti+4 ions into Ti+3 ions. For Li4Ti4.95Ta0.05O12 this reduction is a result of the extra charge of the Ta whereas for Li4Ti5O12 it is a result of nonstoichiometry.